The trivalent oral polio vaccine (Sabin) is a live-attenuated virus vaccine. It is heat-labile and hence must be stored frozen and used soon after thawing to insure effective immunization against poliomyelitis. Although 1 molar magnesium chloride is an effective stabilizer for the Sabin vaccine, inactivation will still occur if the vaccine thaws during transport or storage. Because of the shortage of adequate refrigeration facilities in underdeveloped and tropical regions, where poliovirus is endemic, the vaccine often cannot be stored frozen and as a consequence the vaccine becomes inactivated. This leads to under-immunization of the populations which are most at risk. Thus, eradication of poliomyelitis depends on the ability to assure cold storage and rapid distribution of poliovirus vaccine. Vaccine formulations with improved stability would circumvent this problem.